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SOLID

WHAT’S HE GONNA TALK ABOUT

What is SOLID The S in SOLID The O in SOLID The L in SOLID The I in SOLID The D in SOLID Questions

WHAT’S THIS SOLID BUSINESS

SOLID Principles

Object-Oriented Design

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WHAT’S THIS SOLID BUSINESS

A means to avoid technical debt Decrease Coupling Increase Cohesion

Maintainable Extensible Testable

WHAT’S THIS SOLID BUSINESS

Guidelines, NOT LAWS

You got to know when to hold’em, know when to fold’em,

Know when to walk away and know when to run.-Kenny Rogers

THE REQUEST 1

Application

Flat File

EmailSender•SendEmail•GetMessage

Single Responsibility Principle

SRP

There should never be more than one reason for a class to change

-Uncle Bob

SINGLE RESPONSIBILITY PRINCIPLE

VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE

Application

Flat File

EmailSender•SendEmail•GetMessage

Application

Flat File

FileReader•GetMessage

EmailSender•SendEmail

A REQUEST 2

Application

Flat File

FileReader•GetMessage

EmailSender•SendEmail

XML File

Open-Close Principle

OCP

Software entities (classes, modules, functions, etc…) should be open for extension, but closed for modification

-Uncle Bob

OPEN-CLOSED PRINCIPLE

VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE

Application

Flat File

FileReader

•GetMessage

EmailSender

•SendEmail

XML File

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

REQUEST 3Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

DB File

DbFileReader

•CanRead•ReadFile

Database

Liskov Substitution Principle

LSP

Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it

-Uncle Bob

LISKOV SUBSTITUTION PRINCIPLE

VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

DB File

DbFileReader

•CanRead•ReadFile

Database

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

DbReader

•GetMessage

Database

REQUEST 4Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Database

IReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

DbReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Interface Segregation Principle

ISP

Clients should not be forced to depend upon interfaces that they do not use

-Uncle Bob

INTERFACE SEGREGATION PRINCIPLE

ABIDES BY THE PRINCIPLE

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

EmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Database

IReader

•GetMessage

DbReader

•GetMessage

IFileTypeReaderRegisterable

•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Dependency Inversion Principle

DIP

High level modules should not depend upon low level modules. Both should depend upon abstractions

Abstractions should not depend upon details. Details should depend upon abstractions

-Uncle Bob

DEPENDENCY INVERSION PRINCIPLE

ABIDES BY THE PRINCIPLE

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

IEmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Database

IReader

•GetMessage

DbReader

•GetMessage

IFileTypeReaderRegisterable

•RegisterDefaultFileTypeReader•RegisterFileTypeReader

EmailSender

•SendEmail

WITHOUT SOLID

Application

Flat File

EmailSender•SendEmail•GetMessage

Xml File

Database

WITH SOLID

Application

Flat File

BaseFileTypeReader

•CanRead•ReadFile

IEmailSender

•SendEmail

XML File

FlatFileReader

•CanRead•ReadFile

XmlFileReader

•CanRead•ReadFile

FileReader

•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader

Database

IReader

•GetMessage

DbReader

•GetMessage

IFileTypeReaderRegisterable

•RegisterDefaultFileTypeReader•RegisterFileTypeReader

EmailSender

•SendEmail

QUESTIONS?

REFERENCE LINKS

Martin Folwer – Technical Debt http://www.martinfowler.com/bliki/TechnicalDebt.html

Wikipedia – Coupling http://en.wikipedia.org/wiki/Coupling_(computer_programmi

ng) Wikipedia – Cohesion

http://en.wikipedia.org/wiki/Cohesion_(computer_science) Robert Martin – The Principles of OOD

http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod Derick Bailey – SOLID Principles – Step by step code

https://github.com/derickbailey/presentations-and-training/tree/master/SOLID%20Principles%20-%20Step%20By%20Step%20Code

MY INFORMATION

Email – twang1978@gmail.com Twitter – @tonycwang LinkedIn –

www.linkedin.com/in/tonycwang